Coated conductive particle coated conductive particle manufacturing method anisotropic conductive material and conductive connection structure

ABSTRACT

An objective of the invention is to provide a coated conductive particle having superior connection reliability, a method for manufacturing such coated conductive particle, an anisotropic conductive material and a conductive-connection structure. A coated conductive particle comprising a particle having a surface made of conductive metal and an insulating particles to coat the surface of the particle having the surface made of conductive metal there with, wherein the insulating particles are chemically bonded to the particle having the surface made of conductive metal via a functional group (A) having a bonding property to the conductive metal so that a single coating layer is formed.

TECHNICAL FIELD

The present invention relates to a coated conductive particle havingsuperior connection reliability, a method for manufacturing such coatedconductive particle, an anisotropic conductive material and aconductive-connection structure.

BACKGROUND ART

Particles, each having a metal surface, have been used as various resinfillers, modifying agents and the like, and in addition to these usages,those particles are mixed in a binder resin as conductive particles, andused as so-called anisotropic conductive materials that electricallyconnect miniature-size electrical parts such as semiconductor elementsto circuit boards, or electrically connect circuit boards to each other,in electronic products such as liquid crystal displays, personalcomputers and portable communication devices.

In recent years, along with the developments of miniature-sizeelectronic apparatuses and electronic parts, wires on circuit boards andthe like have become finer, and under these circumstances, conductiveparticles have been made further finer, and the precision of particlesizes has been improved. In order to ensure high connection reliability,it is necessary to increase the blended amount of conductive particlesin an anisotropic conductive material, and in the case of a circuitboard and the like having such fine wires, conduction or the like in alateral direction may occur between adjacent conductive particles tocause problems of short circuit and the like between adjacentelectrodes. In order to solve these problems, an anisotropic conductivematerial, which uses conductive particles of which surfaces are coatedwith an electrical insulating material, has been proposed.

With respect to the method for coating the surfaces of conductiveparticles with an electrical insulating material, for example, JapaneseKokai Publication Hei-4-362104 has disclosed a method in which aninterface polymerizing process, a suspension polymerizing process, anemulsion polymerizing process or the like is carried out in the presenceof conductive particles so that the particles are encapsulated in anelectrical insulating resin, Japanese Kokai Publication Sho-62-40183 hasdisclosed a method for forming microcapsules with an electricalinsulating resin by a dipping process in which conductive particles havebeen dispersed in the resin solution, and then dried, and Japanese KokaiPublication Hei-7-105716 has disclosed methods in which a hybridizationprocess are used for this purpose; and in addition to these methods,methods using vacuum vapor deposition and the like have been known.

In these methods, however, it is difficult to form an insulating coatinglayer with a constant thickness, and in some cases, a plurality ofconductive particles are simultaneously coated. In the case whereconductive connection is made by using coated conductive particles, ifthe thickness of the insulating coating layer is not uniform, a pressureis not transmitted uniformly upon fixing the layer between electrodeseven when the particle size of the conductive particles is preciselycontrolled, with the result that a defective conduction may occur. Forexample, in the case of the above-mentioned formation method of theinsulating coat by the hybridization process, since insulating resinparticles to form a coating layer are made to adhere to the surfaces ofthe conductive particles by a physical force in this method, it is notpossible to form the coating layer on the surface of each of theconductive particles as a single layer, with the result that it becomesdifficult to control the thickness of the insulating coating layer, andsince the resin particles are fused and deformed due to heat and impactcaused by the heating process and frictional heat, it is difficult toprepare an uniform coating layer. Moreover, since the contact areabetween the insulating resin particles and the metal surface becomesgreater, it is difficult to remove the insulating coating layer in thecase where a device to which it is difficult to apply heat and pressure,such as a liquid crystal element, is used, with the result that adefective conduction may occur.

Japanese Kokai Publication Hei-4-259766 and Japanese Kokai PublicationHei-3-112011 have disclosed coated conductive particles in whichinsulating particles are adhered weakly to the surfaces of conductiveparticles by an electrostatic interaction and a hybridization method.However, in the coated conductive particles obtained by these methods,since a bonding force between the insulating particles and theconductive particles, which is dependent only on Van der Waals force orelectrostatic force, is very weak, insulating particles are separatedfrom the conductive particles by dispersion in a binder resin andcontact between adjacent particles. As a result, failing to ensure asufficient insulating property occur.

Moreover, conventionally, upon forming an anisotropic conductivematerial by dispersing such coated conductive particles in a binderresin, those coated conductive particles having a coating layer that isnon-compatible to the binder resin, solvent and the like have been used.For example, Japanese Kokai Publication Hei-4-362104 has disclosed apolymer coating method for metal particles in which a homopolymer layeror a copolymer layer that is non-compatible to a binder resin is formedon the surface of metal particles; Japanese Kokai PublicationSho-62-40183 has disclosed an electrical connecting sheet which isformed by dispersing conductive particles in a hot-melt type insulatingadhesive, and is characterized in that the conductive particles arecoated with a resin that is non-compatible to the hot-melt typeinsulating adhesive; and Japanese Kokai Publication Hei-7-105716 hasdisclosed coated conductive particles each of which is composed of aninsulating core material, a conductive layer formed on the core materialand an insulating layer that covers 0.1 to 99.9% of the area of theconductive layer.

However, when the conductive particles each of which has a coating layerthat is non-compatible to a binder resin are used, affinity in theinterface between the binder resin and the coated conductive particlesbecomes poor, with the result that the coated conductive particlesdispersed in the binder resin may cause a phase separation and the likeand the resulting poor connecting stability. In particular, in the caseof an anisotropic conductive film and an anisotropic conductiveadhesives using thermosetting resin as a binder resin, since theaffinity in the interface between the binder resin and the coatedconductive particles is poor, a separation occurs in the interfacebetween the binder resin and the coated conductive particles after thebinder resin has been cured by thermocompression bonding, failing toensure long-term stability and reliability in connection. Moreover, inthe case where coated conductive particles are dispersed in the binderresin such as a sealing agent or the like in order to maintain a gapbetween the electrodes as well as between liquid crystal panels, sincethe resin used for forming the coating layer is non-compatible to thebinder resin, there is a problem that coated resin thermally fused maybleed out to pollute electrodes, liquid crystal and the like.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a coated conductiveparticle having superior connection reliability, a method formanufacturing a coated conductive particle, an anisotropic conductivematerial and a conductive-connection structure.

A first aspect of the present invention relates to a coated conductiveparticle comprising a particle having a surface made of conductive metaland an insulating particles to coat the surface of the particle havingthe surface made of conductive metal there with, wherein the insulatingparticles are chemically bonded to the particle having the surface madeof conductive metal via a functional group (A) having a bonding propertyto the conductive metal so that a single coating layer is formed. Theparticle having the surface made of conductive metal preferablycomprises a core particle made from a resin and a conductive metal layerformed on the surface of the core particle. The above-mentionedinsulating particles preferably have an average particle size of notmore than 1/10 of the average particle size of the particle having thesurface made of conductive metal and also have a CV value of theparticle size of not more than 20%, and are preferably brought intocontact with the surface of the particle having the surface made ofconductive metal at not more than 20% of the surface area. Moreover, theabove-mentioned insulating particles may be softer than the particlehaving the surface made of conductive metal, and in this case, theparticles may be made from a crosslinking resin. Here, theabove-mentioned insulating particles may be harder than the particlehaving the surface made of conductive metal. Moreover, theabove-mentioned insulating particles preferably have a positive charge,and are preferably made from a resin having an ammonium group or asulfonium group. The functional group (A) having a bonding property tometal is preferably a thiol group or a sulfide group.

In another aspect of the present invention, a method for manufacturingthe coated conductive particle of the first aspect of the presentinvention is provided with at least a step 1 of allowing insulatingparticles to aggregate onto the particle having the surface made ofconductive metal by a Van der Waals force or an electrostatic force inan organic solvent and/or water, and a step 2 of chemically bonding theparticle having the surface made of conductive metal and the insulatingparticles to each other.

A second aspect of the present invention relates to an anisotropicconductive material in which the coated conductive particle of the firstaspect of the present invention is dispersed in an insulating binderresin. The binder resin is preferably an adhesive being cured by heatand/or light. Further, the functional group belonging to the insulatingparticles of the coated conductive particle is preferably chemicallybonded to the functional group in the binder resin, and in this case,the functional group belonging to the insulating particles of the coatedconductive particles to be chemically bonded to the functional group inthe binder resin is preferably an epoxy group. The above-mentionedanisotropic conductive material is preferably an anisotropic conductiveadhesive.

A third aspect of the present invention relates to aconductive-connection structure which is conduction-connected by thecoated conductive particle of the first aspect or the anisotropicconductive material of the second aspect.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a schematic drawing that shows a silicon wafer circuit boardhaving a comb-shaped pattern, which is used in an example.

DETAILED DISCLOSURE OF THE INVENTION

The following description will discuss the present invention in detail.

In accordance with the first aspect of the present invention, each ofthe coated conductive particles comprise particles each having a surfacemade of conductive metal (hereinafter, referred to as metal surfaceparticles), and insulating particles with which the surface of theparticle having the surface made of conductive metal is coated. Withthis arrangement in which the surface of each metal surface particle iscoated with the insulating particles, even in the case where, uponcircuit boards and the like by using the coated conductive particles ofthe first aspect of the present invention, the circuit boards and thelike have fine wires, it is possible to prevent conduction and the likein the lateral direction from occurring by adjacent conductiveparticles, and in the longitudinal direction, the metal surface of themetal surface particle is exposed by carrying out a thermocompressionbonding process by application of heat and pressure so as to positivelymake conduction.

With respect to the above-mentioned metal surface particles, notparticularly limited as long as the outermost surface thereof is made ofconductive metal, examples thereof include: particles made of onlymetal; particles in which a metal layer is formed on the surface of eachof core particles made from an organic compound or an inorganiccompound, by vapor deposition, plating, coating or the like; andparticles in which metal particles are introduced onto the surface ofeach of insulating core particles. Among these, with respect to thoseparticles in which a conductive metal layer is formed on the surface ofeach of core particles made from a resin, when the coated conductiveparticles of the present invention are used for an anisotropicconductive material, those particles are deformed upon contact-bondingelectrodes to each other thereby to increase the contact area, so thatthey are preferably used from the viewpoint of connection stability.

With respect to the above-mentioned metal, not particularly limited aslong as it has conductivity, examples thereof include: metals such asgold, silver, copper, platinum, zinc, iron, tin, lead, aluminum, cobalt,indium, nickel, chromium, titanium, antimony, bismuth, germanium,cadmium and silicon; and metal compounds such as ITO and solder.

The above-mentioned metal layer may have a single-layer structure or alaminated structure having a plurality of layers. In the case of thelaminated structure, the outermost layer is preferably made of gold. Byusing gold as the outermost layer, it becomes possible to provide highcorrosion resistance and small contact resistance, and consequently toachieve superior coated conductive particles.

With respect to the method for forming the conductive metal layer on thesurface of each of the core particles made from a resin, although notparticularly limited, examples thereof include known methods such as aphysical metal vapor deposition method and a chemical electrolessplating method, and from the viewpoint of simple processes, theelectroless plating method is preferably used. With respect to the metallayer formed by the electroless plating process, for example, gold,silver, copper, platinum, palladium, nickel, rhodium, ruthenium, cobalt,tin and alloys of these and the like are exemplified; and in the coatedconductive particles of the present invention, one portion or the entireportion of the metal layer is preferably formed by the electrolessnickel plating, since this method makes it possible to form an uniformcoating layer with high density.

With respect to the method for forming a gold layer as the outermostlayer of the above-mentioned metal layer, not particularly limited, forexample, known methods, such as electroless plating, substitutionplating, electric plating and sputtering, are used.

With respect to the thickness of the metal layer, although notparticularly limited, the lower limit value is preferably set to 0.005μm, and the upper limit value is preferably set to 1 μm. In the case ofthe thickness of less than 0.005 μm, it sometimes becomes difficult toobtain sufficient effects as the conductive layer, and in the case ofthe thickness of more than lam, the specific gravity of the resultingcoated conductive particles becomes too high, or the hardness of thecore particles made from a resin becomes too high to be sufficientlydeformed. The lower limit value is more preferably set to 0.01 μm, andthe upper limit value is more preferably set to 0.3 μm.

Moreover, in the case where a gold layer is used as the outermost layerof the above-mentioned metal layer, the lower limit of the thickness ofthe gold layer is preferably set to 0.001 μm, and the upper limitthereof is preferably set to less than 0.5 μm. In the case of thethickness of less than 0.00 μm, it becomes difficult to coat the metallayer uniformly, with the result that the improved effects in corrosionresistance and contact resistance value are no longer achieved, and inthe case of the thickness of more than 0.5 μm, the layer becomesexpensive in comparison with its effects. The lower limit value is morepreferably set to 0.01 μm, and the upper limit value is more preferablyset to 0.1 μm.

In the case where each of the metal surface particles comprise a coreparticle made from an organic compound and a metal layer formed on thesurface thereof, not particularly limited, the core particles are madefrom, for example, polyolefins such as polyethylene, polypropylene,polystyrene, polypropylene, polyisobutylene and polybutadiene, acrylicresins such as polymethylmethacrylate and polymethylacrylate,polyalkylene terephthalate, polysulfone, polycarbonate, polyamide,phenolic resins such as phenol formaldehyde resin, melamine resins suchas melamine formaldehyde resin, benzoguanamine resins such asbenzoguanamine formaldehyde resin, urea formaldehyde resin, epoxyresins, (un)saturated polyester resins, polyethylene terephthalate,polysulfone, polyphenylene oxide, polyacetal, polyimide, polyamidimide,polyetherether ketone, polyether sulfone, and the like. Among these,those core particles, which are made from a resin formed by polymerizingone kind or two kinds or more of various polymerizable monomers havingan ethylenic unsaturated group, are preferably used since they easilyprovide a preferable hardness.

The polymerizable monomer having an ethylenic unsaturated group may be anon-crosslinking monomer or a crosslinking monomer.

With respect to the non-crosslinking monomer, examples thereof include:styrene-based monomers, such as styrene, α-methylstyrene,p-methylstyrene, p-chlorostyrene and chloromethylstyrene;carboxylic-group containing monomers such as (meth)acrylic acid, maleicacid and maleic anhydride; alkyl(meth)acrylates such as methyl(meth)acrylate, ethyl (meth)acrylate, propyl(meth)acrylate,butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, lauryl(meth)acrylate,cetyl(meth)acrylate, stearyl(meth)acrylate, cyclohexyl(meth)acrylate,isobornyl(meth)acrylate, ethylene glycol(meth)acrylate,trifluoroethyl(meth)acrylate and pentafluoropropyl(meth)acrylate;oxygen-atom-containing (meth)acrylates such as2-hydroxyethyl(meth)acrylate, glycerol(meth)acrylate,polyoxyethylene(meth)acrylate and glycidyl(meth)acrylate;nitrile-containing monomers such as (meth)acrylonitrile; vinyl etherssuch as methyl vinyl ether, ethyl vinyl ether and propyl vinyl ether;acid vinyl esters such as vinyl acetate, vinyl butyrate, vinyl laurate,vinyl stearate, vinyl fluoride, vinyl chloride and vinyl propionate; andunsaturated hydrocarbons such as ethylene, propylene, butylene, methylpentene, isoprene and butadiene.

With respect to the above-mentioned crosslinking monomers, examplesthereof include: multifunctional (meth)acrylates, such astetramethylolmethane tetra(meth)acrylate, tetramethylolmethanetri(meth)acrylate, tetramethylolmethane di(meth)acrylate,trimethylolpropane tri(meth)acrylate, dipentaerythritolhexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, glyceroltri(meth)acrylate, glycerol di(meth)acrylate, polyethylene glycoldi(meth)acrylate and polypropylene glycol di(meth)acrylate; diallylethers such as triallyl (iso)cyanurate, triallyl trimellitate, divinylbenzene, diallyl phthalate and diallyl acrylamide; silane-containingmonomers such as γ-(meth)acryloxypropyl trimethoxysilane, trimethoxysilylstyrene and vinyl trimethoxysilane; dicarboxylic acids such asphthalic acid; diamines; diallyl phthalate, benzoguanamine, triallylisocyanate and the like.

The lower limit of the average particle size of the above-mentioned coreparticles is preferably set to 0.5 μm, and the upper limit thereof ispreferably set to 100 μm. When the average particle size is less than0.5 μm, aggregation may occur upon forming a metal layer, with theresult that the resulting coated conductive particles, manufactured byusing the core particles having the aggregation, may causeshort-circuiting between adjacent electrodes, and when the averageparticle size is more than 100 μm, the metal layer of the resultingcoated conductive particles is susceptible to separation, resulting inpoor connecting reliability. The lower limit is more preferably set tolam, and the upper limit is more preferably set to 20 μm. Here, theaverage particle size of the above-mentioned core particles can be foundby statistically processing particle sizes measured by using an opticalmicroscope, an electronic microscope, a Coulter Counter and the like.

The variation coefficient of the average particle size of the coreparticles is preferably set to not more than 10%. The variationcoefficient of more than 10% makes it difficult to desirably control thegap between electrodes that face each other by using the resultingcoated conductive particles. Here, the term, “variation coefficient”,used herein refers to a numeric value obtained by dividing the standarddeviation derived from the particle-size distribution by the averageparticle size.

The lower limit of the 10% K value of the above-mentioned core particlesis preferably set to 1000 MPa, and the upper limit thereof is preferablyset to 15000 MPa. When the value is less than 1000 MPa, the strength ofthe resulting coated resin particles becomes insufficient; therefore,when compressed and deformed, the particles may be broken, failing toexert functions as a conductive material. In contrast, when the value ismore than 15000 MPa, the electrodes may be damaged. The lower limit ismore preferably set to 2000 MPa, and the upper limit is more preferablyset to 10000 MPa. Here, the above-mentioned 10% K value is obtained bytesting processes in which: a minute compression tester (for example,PCT-200 made by Shimadzu Corporation, and the like) is used, andparticles are compressed by the end face of a smooth indenter formed bya column made of diamond with a diameter of 50 μm, under conditions of acompression rate of 2.6 mN/sec and a maximum test load of 10 g so that acompression dislocation (mm) is measured, and the corresponding value isobtained by the following equation:K value(N/mm²)=(3/√2)·F·S ^(−3/2) ·R ^(−1/2)

F: load value (N) in 10% compression deformation of particles

S: compression dislocation (mm) in 10% compression deformation ofparticles

R: radius (mm) of particles

Here, in order to obtain core particles of which 10% K value satisfiesthe above-mentioned conditions, the core particles are preferably formedby a resin that is prepared by polymerizing the above-mentionedpolymerizable monomer having an ethylenic unsaturated group, and in thiscase, at least not less than 20 weight % of the cross-linking monomer ispreferably contained therein as a constituent component.

The core particles are preferably allowed to have a recovery rate of notless than 20%. In the case of the recovery rate of less than 20%, since,upon compressing the resulting coated conductive particles, the deformedparticles fail to return to its original state, defective connection mayoccur. The recovery rate is more preferably set to not less than 40%.Here, the above-mentioned recovery rate refers to a recovery rateobtained after imposing a load of 9.8 mN to the particles.

With respect to the above-mentioned insulating particles, notparticularly limited as long as the particles have an insulatingproperty, examples thereof include those particles made from aninsulating inorganic substance such as silica, in addition to thoseparticles made from an insulating resin. Among these, those particlesmade from an insulating resin are preferably used. With respect to theabove-mentioned insulating resin, not particularly limited, for example,those resins for use in the above-mentioned core particles may be used.These resins may be used alone, or two or more kinds thereof may be usedin combination.

Although varied depending on the particle size of the metal surfaceparticles and the applications of the coated conductive particles, theparticle size of the insulating particles is preferably set to not morethan 1/10 of the particle size of the metal surface particles. In thecase of the particle size of more than 1/10, the particle size of theinsulating particles becomes too great, with the result that the effectsof the application of the metal surface particles are no longerexpected. Moreover, in the case of the particle size of not more than1/10, upon manufacturing the coated conductive particles of the presentinvention by a hetero-aggregation method, it is possible to effectivelyadsorb the insulating particles onto the metal surface particles.Moreover, in the case where the coated conductive particles of thepresent invention are used as an anisotropic conductive material, theparticle size of the insulating particles is preferably set in a rangefrom 5 to 1000 nm. In the case of the particle size of less than 5 nm,since the distance between the adjacent coated conductive particlesbecomes smaller than a hopping distance of electrons, leaking may occur,and in the case of the particle size of more than 1000 nm, a pressureand heat required upon thermocompression bonding become too great. Morepreferably, the particle size is set in a range from 10 to 500 nm.

Additionally, two kinds of insulating particles having respectivelydifferent particle sizes may be used in combination since thisarrangement allows smaller insulating particles to enter gaps formedbetween greater insulating particles serving as a coating layer toimprove the coating density. In this case, the particle size of thesmaller insulating particles is preferably set to not more than ½ of theparticle size of the larger insulating particles, and the number of thesmaller insulating particles is preferably set to not more than ¼ of thenumber of the larger insulating particles.

The above-mentioned insulating particles are preferably allowed to havea CV value of the particle size of not more than 20%. In the case of theCV value of more than 20%, the thickness of the resulting coating layerof the coated conductive particles becomes nonuniform, with the resultthat it becomes difficult to apply a pressure uniformly upon conductingthermocompression-bonding processes between electrodes, and thesubsequent defective conduction may occur. Here, the CV value of theabove-mentioned particle size is calculated from the following equation:CV value (%) of particle size=standard deviation of particlesize/average particle size×100

With respect to the measuring method for the above-mentionedparticle-size distribution, prior to the coating of the metal surfaceparticles, measurements can be carried out by using a grain-sizedistribution meter or the like, and after the coating thereof,measurements can be carried out by using an image analysis or the likeof SEM photographs.

With respect to the above-mentioned insulating particles, preferably,not more than 20% of the surface area is brought into contact with thesurface of each of the metal surface particles. In the case of the valueof more than 20%, the deformation of the insulating particles becomesgreater, making the thickness of the coating layer of the resultingcoated conductive particles nonuniform, or making the bonding forcebetween the insulating particles and the metal surface particles toostrong; thus, even when contact-bonding processes are carried outbetween the electrodes, the insulating particles are not removed, withthe result that defective conduction may occur. Here, with respect tothe lower limit, not particularly limited, it may be virtually set to 0%in the case where the insulating particles and the metal surfaceparticles are bonded by, for example, a polymer having a long chain, orthe like.

The above-mentioned insulating particles are preferably allowed to havea positive charge. When the particles have a positive charge, it ispossible to bond them to the metal surface particles by a heteroaggregation method, which will be described later, and since theabove-mentioned insulating particles are made electrostaticallyrepulsive from one another, it becomes possible to prevent theinsulating particles from mutually aggregating with one another, andconsequently to form a single coating layer. In other words, when theinsulating particles are positively charged, the insulating particlesare allowed to adhere onto each of the metal surface particles as asingle layer. Moreover, in the case where such a positive charge isderived from an ammonium group or a sulfonium group, this group alsoserves as a functional group (A) having a bonding property to metal,which will be described later, allowing the insulating particles todirectly form a chemical bond to the metal of the surface of each of themetal surface particles with ease. Therefore, the above-mentionedinsulating particles are preferably made from a resin having an ammoniumgroup or a sulfonium group. In particular, the particles are morepreferably made from a resin containing a sulfonium group.

With respect to the insulating particles having a positive charge,examples thereof include those formed by mixing a polymerizable monomerhaving a positive charge therein upon manufacturing the insulatingparticles, those formed by a polymerizing process using a radicalinitiator having a positive charge and those formed by using adispersion stabilizer or an emulsifier having a positive charge. Two ormore kinds of these may be used in combination. Among these, the methodusing a polymerizable monomer having a positive charge or the methodusing a radical initiator is preferably adopted.

With respect to the polymerizable monomer having a positive charge,examples thereof include: ammonium-containing monomers such asN,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropyl acrylamideand N,N,N-trimethyl-N-2-methacryloyloxyethyl ammonium chloride, andmonomers having a sulfonium group, such as methacrylic acidphenyldimethylsulfoniummethyl sulfate. With respect to the radicalinitiator having a positive charge, examples thereof include:2,2′-azobis{2-methyl-N-[2-(1-hydroxy-butyl)]-propion amide},2,2′-azobis[2-(2-imidazoline-2-yl)propane],2,2′-azobis(2-amidinopropane) and salts of these.

With respect to the coated conductive particles of the first aspect ofthe present invention, the above-mentioned metal surface particles andthe insulating particles are chemically bonded via a functional group(A) having a bonding property to metal. The chemical bond provides agreater bonding force in comparison with a bonding force derived fromonly Van der Waals force and electrostatic force so that it becomespossible to prevent the separation of insulating particles from themetal surface particles when dispersed in a binder resin or the like aswell as separation to cause leaking upon contact with the adjacentparticles when the coated conductive particles are used as ananisotropic conductive material. Moreover, the chemical bond is formedonly between the metal surface particles and the insulating particles,with no insulating particles being mutually bonded; therefore, thecoating layer is formed by the insulating particles as a single layer.For this reason, when particles having properly adjusted particle sizesare used as the metal surface particles and the insulating particles, itis possible to easily prepare an uniform particle size for the coatedconductive particles of the present invention.

With respect to the above-mentioned functional group (A), notparticularly limited as long as it is capable of forming an ionic bond,a covalent bond or a coordinate bond with metal, examples thereofinclude: a silane group, a silanol group, a carboxyl group, an aminogroup, an ammonium group, a nitro group, a hydroxyl group, a carbonylgroup, a thiol group, a sulfonic acid group, a sulfonium group, a boricacid group, an oxazoline group, a pyrrolidone group, a phosphoric acidgroup and a nitrile group. Among these, those functional groups capableof forming a coordinate bond are preferably used, and functional groupshaving S, N or P atoms are preferably used. For example, in the casewhere gold is used as the metal, those functional groups having S atomsthat form a coordinate bond to gold, such as a thiol group and a sulfidegroup, are more preferably used.

With respect to the method for allowing the metal surface particles andthe insulating particles to be chemically bonded to each other by usingfunctional group (A), although not particularly limited, for example, 1)a method for introducing insulating particles, each having functionalgroup (A) on its surface, onto the surface of each of the metal surfaceparticles, and 2) a method in which functional group (A) and a compoundhaving a reactive functional group (B) are directed onto the metalsurface and each functional group (B) is allowed to react with theinsulating particles by one step or multiple steps of reactions so as tobe bonded to each other may be proposed.

With respect to the above-mentioned method 1), in the method for formingthe insulating particles having functional group (A) on the surfacethereof, not particularly limited, examples thereof include a method formixing a monomer having functional group (A) in the insulating particlesupon manufacturing the insulating particles; a method for directingfunctional group (A) to the surface of each of the insulating particlesby a chemical bond; a method for chemically processing the surface ofeach of the insulating particles so that the surface is modified to havefunctional group (A); and a method for modifying the surface of each ofthe insulating particles to have functional group (A) by a plasmatreatment or the like.

With respect to the above-mentioned method 2), for example, a method isproposed in which: a compound, which has functional group (A) andreactive functional group (B), such as hydroxyl group, carboxyl group,amino group, epoxy group, silyl group, silanol group and isocyanategroup, in the same molecule is allowed to react with the metal surfaceparticles, and this is then allowed to react with organic compoundparticles, each having a functional group capable of forming a covalentbond with reactive functional group (B) on its surface. With respect tothe compound having functional group (A) and reactive functional group(B) in the same molecule, examples thereof include 2-aminoethane thioland p-aminothiophenol. In the case where 2-aminoethane thiol is used,2-aminoethane thiol is bonded to the surface of each of the metalsurface particles via an SH group, with an amino group on the other sidebeing allowed to react with, for example, insulating particles, eachhaving an epoxy group, a carboxyl group or the like on its surface;thus, it becomes possible to bond the metal surface particles to theinsulating particles.

When the connecting processes between electrodes are carried out byusing the coated conductive particles of the first aspect of the presentinvention, a thermocompression-bonding process is conducted by applyingheat and a pressure so that the metal surface of each of the metalsurface particles is exposed so as to allow conduction. Here, theexpression, “the metal surface is exposed”, refers to a state in whichthe metal surface of the metal surface particles is directly broughtinto contact with the electrode without being interrupted by theinsulating particles. With respect to conditions for the above-mentionedthermocompression-bonding, although not necessarily limited depending onthe density of the coated conductive particles in the anisotropicconductive material and the kinds of the electronic parts to beconnected, the temperature is normally set in a range from 120 to 220°C. with the pressure being set in a range from 9.8×10⁴ to 4.9×10⁶ Pa.

With respect to the mode in which the metal surface of each of the metalsurface particles is exposed, the following three modes are considered.

The first mode is prepared as an arrangement in which uponthermocompression-bonding, the insulating particles are fused so thatthe metal surface of each of the metal surface particles is exposed.

The second mode is prepared as an arrangement in which uponthermocompression-bonding, the insulating particles are deformed so thatthe metal surface of each of the metal surface particles is exposed.

The third mode is prepared as an arrangement in which uponthermocompression-bonding, the metal surface particles and theinsulating particles are separated from each other so that the metalsurface of each of the metal surface particles is exposed.

Among these, it is preferable to use the second mode to expose the metalsurface of each of the metal surface particles so as to allow conductiveconnection. In the case of the first mode, the fused insulatingparticles may bleed out to pollute the binder resin and the circuitboards, or the coating layer for insulating the gap between the adjacentcoated conductive particles is also fused, failing to provide asufficient insulating property, and in the case of the third mode, when,upon thermocompression-bonding, the metal surface particles and theinsulating particles are aligned in the contact-bonding direction, theinsulating particles are sandwiched between the metal surface particlesand the circuit board, and are not separated in some cases, resulting indegradation in connection reliability.

As to which mode is used to expose the metal surface of each of themetal surface particles to allow conductive connection, normally, it iscontrolled based upon on the relative relationship between the hardnessof the metal surface particles and the hardness of the insulatingparticles, although it depends on thermocompression-bonding conditionsand the like. Here, the term, “the hardness of the particles”, refers toa relative hardness under a thermocompression-bonding condition, and forexample, in the case where the softening temperature of the insulatingparticles is low in comparison with the metal surface particles and whenonly the insulating particles are allowed to soften under thethermocompression-bonding condition, the insulating particles arerelatively softer.

In the case where the insulating particles are relatively softer thanthe metal surface particles, normally, the above-mentioned first orsecond mode is used so that the metal surface of each of the metalsurface particles is exposed to allow conductive connection. In otherwords, for example, when those particles having a melting point lowerthan the thermocompression-bonding temperature are used as theinsulating particles, the insulating particles are softer under thethermocompression-bonding condition, with the result that the insulatingparticles are fused to flow, thereby exposing the metal surface of eachof the metal surface particles. Further, when those particles which havea melting point higher than the thermocompression-bonding temperature,but have a softening point lower than the thermocompression-bondingtemperature are used as the insulating particles, the insulatingparticles are softer under the thermocompression-bonding condition, theinsulating particles are deformed and broken, thereby exposing the metalsurface of each of the metal surface particles. With respect to suchmaterials that have a melting point higher than thethermocompression-bonding temperature, but have a softening point lowerthan the thermocompression-bonding temperature, examples thereofinclude: crosslinking resins; and rubbers such as natural rubber andsynthesized rubber.

In contrast, in the case where the insulating particles are harder thanthe metal surface particles, normally, the above-mentioned third mode isused so that the metal surface of each of the metal surface particles isexposed to allow conductive connection. In other words, for example,when such coated conductive particles are placed between electrodes to athermocompression-bonding process, a stress is exerted between the metalsurface particles and the insulating particles due to thecontact-bonding process, and when this stress is more than the bondingforce derived from the chemical bonding, the insulating particles arereleased from each of the metal surface particles, with the result thatthe metal surface of each of the metal surface particles is exposed.

With respect to the relative relationship between the hardness of themetal surface particles and the hardness of the insulating particles,for example, in the case where particles comprising core particles madefrom a resin and a conductive metal layer that is formed on the surfaceof each of the core particles are used as the above-mentioned metalsurface particles, with a resin having an insulating property being usedas the insulating particles, the adjustments can be made by properlyselecting a) a kind of resin to be used as the core particles of themetal surface particles and a kind of resin to be used as the insulatingparticles; b) a crosslinking degree of the resin to be used as the coreparticles of the metal surface particles and a crosslinking degree ofthe resin to be used as the insulating particles; and c) a kind of metaland a thickness of a metal layer used for the metal surface particlesand a kind of resin to be used as the insulating particles.

Here, in order to expose the metal surface of each of the metal surfaceparticles, the coating rate of the insulating particles, that is, thearea occupied by a portion coated with the insulating particles in theentire surface area of each of the metal surface particles, ispreferably set in a range from 5 to 50%. In the case where the area isless than 5%, the adjacent coated conductive particles may mutually havean insufficient insulating property; in contrast, in the case where thearea is more than 50%, with respect to the first mode, the amount ofinsulating particles to be fused and removed increases, with the resultthat heat and pressure need to be applied in a manner so as to be morethan the required levels and that the removed resin may causedegradation in performances of the binder resin; with respect to thesecond mode, even if the insulating particles are deformed and broken,the metal surface sometimes is not sufficiently exposed; and withrespect to the third mode, in order to push the adjacent insulatingparticles aside to separate the insulating particles in thethermocompression-bonding direction, a pressure needs to be applied in amanner so as to be more than the required level, and the insulatingparticles may be sandwiched between the metal surface particles and theelectrodes, causing a higher possibility of defective conduction.

The following description will further discuss adjustments of therelative relationship between the hardness of such metal surfaceparticles and the hardness of such insulating particles. For example, inthe case where those particles that are made from a comparatively hardmaterial, such as a comparatively hard metal like copper, nickel, ironand gold; a comparatively hard metal compounds like aluminum nitride;inorganic particles like silica; or a material composed of a coreparticle made from a resin in which the blended amount of a crosslinkingmonomer is not less than 50% by weight, and a metal layer formedthereon, are selected as the above-mentioned metal surface particles,the following materials are selected as the above-mentioned insulatingparticles so that an alignment is properly made as to which mode is usedfor exposing the metal surface of each of the metal surface particles toallow conductive connection.

In other words, for example, when a resin which has a blended amount ofa crosslinking monomer of less than 1% by weight and a meltingtemperature in a range from 60 to 220° C. is selected as the insulatingparticles, the first mode is presumably adopted so that the metalsurface of each of the metal surface particles is exposed to allowconductive connection. In this case, the gel fraction of the insulatingparticles is preferably set to not more than 50%. With respect to thematerial for such insulating particles, for example, a methylmethacrylate/styrene copolymer containing about 0.5% by weight ofdivinyl benzene or ethylene glycol dimethacrylate as crosslinkingmonomers is proposed. Here, when the melting temperature is less than60° C., the coated conductive particles may be adhered with one anotherupon transportation and storage. Moreover, in the case where the blendedamount of the crosslinking monomer is 0%, the particles may be dissolvedin an organic solvent upon dispersing a binder resin and the like.

Moreover, for example, when a resin which has a blended amount of acrosslinking monomer of 1 to 20% by weight and a softening temperatureof 60 to 220° C. is selected as the material for the insulatingparticles, the second mode is presumably adopted so that the metalsurface of each of the metal surface particles is exposed to allowconductive connection. In this case, the gel fraction of the insulatingparticles is preferably set to not less than 50%. With respect to thematerial for such insulating particles, for example, a methylmethacrylate/styrene copolymer containing about 3% by weight of divinylbenzene as a crosslinking monomer, and a resin containing about 5% byweight of divinyl benzene or ethylene glycol dimethacrylate areproposed.

Furthermore, for example, when a resin, which have a blended amount of acrosslinking monomer of not less than 50% by weight and are not softenedand inorganic particles, are selected as the materials for theinsulating particles, the third mode is presumably adopted so that themetal surface of each of the metal surface particles is exposed to allowconductive connection. In this case, the gel fraction of the insulatingparticles is preferably set to not less than 80%. With respect to thematerial for such insulating particles, for example, a resin containingabout 80% by weight of divinyl benzene and pentaerythritol tetracrylateas crosslinking monomers, silica, aluminum nitride and the like areproposed.

Among these, a combination of a resin containing not less than 50% byweight of a crosslinking monomer serving as core particles, metalsurface particles having a nickel/gold layer as a metal layer andinsulating particles made from a styrene copolymer resin containing 2 to5% by weight of a multifunctional (meth)acrylate, such as divinylbenzene, ethylene glycol dimethacrylate and pentaerythritoltetracrylate, as crosslinking monomers is one of the most superiormaterial from the viewpoint of connection reliability, and morepreferably used.

With respect to the method for forming the coated conductive particlesin accordance with the first aspect of the present invention, althoughnot particularly limited as long as it is a method for allowing theabove-mentioned insulating particles to contact the surface of each ofthe metal surface particles to be chemically bonded thereto, forexample, a method, which includes a step 1 in which at least insulatingparticles are allowed to aggregate on each of particles that has asurface made from conductive metal by a Van der Waals force or anelectrostatic interaction in an organic solvent and/or water and a step2 in which the particle having the surface made from conductive metaland the insulating particles are chemically bonded to each other, ispreferably used. The aggregation method of step 1 is referred to as ahetero aggregation method, and since this method ensures a swiftchemical reaction between the metal surface particles and the insulatingparticles by solvent effects, it is not necessary to apply an excessivepressure and it is possible to easily control the temperature of theentire system; therefore, the insulating particles are less susceptibleto deformation or the like due to heat. In contrast, when the insulatingparticles are directed by a conventional dry method using a high-speedstirrer, a hybridizer or the like, an excessive pressure or load such asfrictional heat may be applied; consequently, in the case where theinsulating particles are harder than the metal surface particles, themetal surface particles may be damaged or the metal layer may beseparated, and in the case where the insulating particles are softerthan the metal surface particles and when the glass transitiontemperature of the insulating particles is low, the insulating particlesare deformed due to collision against the metal surface particles andfrictional heat, causing disadvantages that the contact area becomeslarger, that the insulating layer thickness becomes nonuniform, that theinsulating particles are laminated and stacked and that the insulatingparticles are fused to make the coated conductive particles joined toeach other to fail to form a single particle.

With respect to the organic solvent, any solvent may be used withoutlimitation as long as it does not dissolve the insulating particles.

Another aspect of the present invention, which relates to the method formanufacturing the coated conductive particles of the first aspect of thepresent invention, provides a method which comprises at least the stepsof a step 1 of allowing insulating particles to aggregate onto theparticle having the surface made of conductive metal by a Van der Waalsforce or an electrostatic interaction in an organic solvent and/orwater; and a step 2 of chemically bonding the particle having thesurface made of conductive metal and the insulating particles to eachother.

In the coated conductive particles of the first aspect of the presentinvention, since the metal surface particles and the insulatingparticles are chemically bonded to each other, it is possible to preventthe insulating particles from separation due to a weak bonding forcebetween the insulating particles and the metal surface, upon dispersingthem with a binder resin and the like and upon allowing them to contactthe adjacent particles. Moreover, since the insulating particles form asingle coating layer and have a small particle-size distribution of theinsulating particles, and since the contact area between the insulatingparticles and the metal surface is constant, it is possible to providean uniform particle size with respect to the coated conductiveparticles.

In the case where the coated conductive particles of the first aspect ofthe present invention are used as an anisotropic conductive material, itbecomes possible to expose the metal surface of the metal surfaceparticles by a thermocompression-bonding process upon connection toensure positive conduction, and since it is possible to prevent theinsulating particles from coming off the surface of each of the metalsurface particles uniform by a pressure imposed between the adjacentparticles, and consequently to ensure a positive insulating property.

The coated conductive particles of the first aspect of the presentinvention are used for applications such as an anisotropic conductivematerial, a heat-ray reflection material and an electromagnetic-waveshielding material. Among these, when dispersed in an insulating binderresin, the coated conductive particles are desirably used as ananisotropic conductive material.

A second aspect of the present invention relates to an anisotropicconductive material formed by dispersing the coated conductive particlesof the first aspect of the present invention in an insulating binderresin. In the present specification, the anisotropic conductive materialincludes an anisotropic conductive film, an anisotropic conductivepaste, an anisotropic conductive adhesive, an anisotropic conductive inkand the like.

With respect to the method for forming the above-mentioned anisotropicconductive film, not particularly limited, for example, a method isproposed in which the coated conductive particles of the presentinvention are suspended in a solvent to which a binder resin has beenadded, this suspended solution is put and drawn on a mold-releasing filmto form a coat film, and the resulting film formed by evaporating thesolvent from the coat film is wound up onto a roll. Upon conductiveconnection by the use of the above-mentioned anisotropic conductivefilm, the coat film is drawn out together with the mold-releasing film,and the coat film is put on an electrode to which it is bonded, and anopposing electrode is superposed on this to be connected thereto by athermocompression-bonding process.

The above-mentioned anisotropic conductive paste is prepared, forexample, by forming an anisotropic conductive adhesive into paste, andthis is loaded into an appropriate dispenser, and applied onto anelectrode to be connected with a desired thickness, and an opposingelectrode is superposed on this and the resin is cured by athermocompression-bonding process so that the connection is made.

The above-mentioned anisotropic conductive ink is prepared by, forexample, by adding a solvent to an anisotropic conductive adhesive toprovide appropriate viscosity for printing, and this is screen-printedon an electrode to be bonded, and the solvent is then evaporated, and anopposing electrode is superposed on this and subjected to athermocompression-bonding process so that the connection is made.

With respect to the film thickness of the coat film of theabove-mentioned anisotropic conductive material, preferably,calculations are conducted based upon the average particle size of thecoated conductive particles of the present invention to be used and thespecification of the electrodes to be connected so that the coatedconductive particles are properly sandwiched between the electrodes tobe connected, with a gap between joining circuit boards beingsufficiently filled with the adhesive layer.

With respect to the insulating binder resin, not particularly limited aslong as it has an insulating property, examples thereof include:

thermoplastic resins such as acrylates, ethylene-vinyl acetate resins,styrene-butadiene block copolymers and hydrogenated products thereof;styrene-isoprene block copolymers and hydrogenated products thereofthermosetting resins such as epoxy resins, acrylate resins, melamineresins, urea resins and phenolic resins; and resins to be cured byultraviolet rays and electron beams, such as acrylates of polyhydricalcohol, polyester acrylates and unsaturated esters of polyhydriccarboxylic acid. Among these, adhesives which are cured by heat and/orlight are preferably used.

In the anisotropic conductive material in accordance with the secondaspect of the present invention, a functional group contained in theinsulating particles of the coated conductive particles of the firstaspect of the present invention to be contained therein is preferablychemically bonded to a functional group in a binder resin. Theabove-mentioned insulating particles and the binder resin are chemicallybonded to each other so that the coated conductive particles of thefirst aspect of the present invention, dispersed in the binder resin,are allowed to have superior stability, and so that it is possible toprevent thermally-fused insulating particles from bleeding out topollute electrodes and liquid crystal; thus, it becomes possible toprepare an anisotropic conductive material that is superior in long-termconnection stability and reliability.

With respect to the combination between such insulating particles andthe binder resin, the insulating particles are preferably allowed tohave a functional group such as carboxyl group, epoxy group, isocyanategroup, amino group, hydroxyl group, sulfone group, silane group andsilanol group, and among these, the insulating particles preferablycontain epoxy group. In contrast, with respect to the binder resin, a(co)polymer, which has a functional group capable of reacting with thesefunctional groups at normal temperature, under heat or upon irradiationwith light, and a monomer or the like, which has the above-mentionedreactive functional group, and forms a (co)polymer and apoly-condensation product by a polymerizing reaction or a polycondensingreaction, are preferably used. These binder resins may be used alone, ortwo or more kinds of these may be used in combination.

With respect to the above-mentioned (co)polymer, not particularlylimited, examples thereof include:

polyolefins such as polyethylene and polybutadiene; polyethers such aspolyethylene glycol and polypropylene glycol; polystyrene,poly(meth)acrylic acid, poly(meth)acrylate, polyacrylamide, polyvinylalcohol, polyvinyl ester, phenolic resin, melamine resin, allyl resin,furan resin, polyester, epoxy resin, silicone resin, polyimide resin,polyurethane, fluororesin, acrylonitrile-styrene copolymer resin,styrene-butadiene copolymer resin, vinyl resin, polyamide resin,polycarbonate, polyacetal, polyether sulfone, polyphenylene oxide,sugar, starch, cellulose and polypeptide. These (co)polymers may be usedalone, or two or more kinds of these may be used in combination.

Moreover, with respect to the monomer capable of forming theabove-mentioned (co)polymer and polycondensation product, notparticularly limited, examples thereof include a vinyl-based monomerthat carries out a polymerizing reaction by using, for example, heat,light, an electron beam, a radical polymerization initiator, apolymerization catalyst or the like, and a monomer that carries out apolycondensation reaction. These monomers may be used alone or two ormore kinds of these may be used in combination.

In addition to the binder resin and the coated conductive particles ofthe first aspect of the present invention that are essential components,to the anisotropic conductive material of the second aspect of thepresent invention, for example, one or two or more kinds of thefollowing various additives may be added within a range so as not toimpair the objectives of the present invention: a filler, an extender, asoftener, a plasticizer, a polymerizing catalyst, a curing catalyst, acolorant, an antioxidant, a thermal stabilizer, a light-stabilizer, anultraviolet-ray absorbing agent, a lubricant, an antistatic agent and anon-flammable agent.

With respect to the method for dispersing the coated conductiveparticles of the first aspect of the present invention in theabove-mentioned binder resin, not particularly limited, conventionallyknown dispersing methods may be used; and the following methods areproposed: dispersion methods in which a mechanical shearing force isapplied, such as a method in which, after coated conductive particleshave been added to a binder resin, this mixture is dispersed by aplanetary mixer or the like so that the particles are dispersed; amethod in which, after coated conductive particles have been uniformlydispersed in water or an organic solvent by using a homogenizer or thelike, this dispersion solution is added to a binder resin and kneaded bya planetary mixer or the like to be dispersed; and a method in which,after a binder resin has been diluted by water, an organic solvent orthe like, coated conductive particles are added to this solution, anddispersed and dispersed by using a planetary mixer or the like. Thesedispersing methods may be used alone or two or more kinds of these maybe used in combination.

With respect to the method for applying a mechanical shearing force, notparticularly limited, for example, various mixing and stirring devices,such as a planetary stirrer, an universal stirrer, a planetary mixer, aroll, a propeller stirrer and a disper, and various mixing and stirringmethods using these devices are used. Here, upon applying theabove-mentioned mechanical shearing force, preferably, a method andconditions are properly selected so as not to apply such a greatmechanical shearing force as to damage the structure of the coatedconductive particle of the first aspect of the present invention to bedispersed in the binder resin.

With respect to the mode of the anisotropic conductive material of thesecond aspect of the present invention, not particularly limited, forexample, an insulating liquid-state or solid-state adhesive is used as abinder resin, and coated particles of the present invention aredispersed in this adhesive; thus, an amorphous anisotropic conductiveadhesive may be formed and applied, or a regular-shape anisotropicconductive film may be used.

A third aspect of the present invention relates to aconductive-connection structure formed by conductive-connectingelectronic parts such as IC chips and circuit boards by using the coatedconductive particles of the first aspect of the present invention or theanisotropic conductive material of the second aspect of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in more detail by way ofexamples, but the invention is not restricted only to these examples.

1. Preparation of Insulating Particles [1] to [8]

(1) Preparation of Insulating Particles [1]

To distilled water in a separable flask (1000 mL) equipped with afour-neck separable cover, a stirring blade, a three-way stopcock, acondenser and a temperature probe was added a monomer compositioncomposed of 100 mmol of methyl methacrylate, 1 mmol ofN,N,N-trimethyl-N-2-methacryloyloxyethyl ammonium chloride and 1 mmol of2,2′-azobis(2-amidinopropane) dihydrochloride so that its solidcomponent content was set to 5% by weight therein, and this was thenstirred at 200 rpm, and subjected to a polymerizing process at 70° C. ina nitrogen atmosphere for 24 hours. After completion of the reaction,the resulting matter was frozen and dried to prepare insulatingparticles [1] having an average particle-size of 220 nm and a CV valueof the particle size of 10%, with an ammonium group being contained inthe surface thereof.

(2) Preparation of Insulating Particles [2]

The same preparation processes as the insulating particles [1] werecarried out except that the monomer composition was changed to contain50 mmol of styrene, 50 mmol of glycidyl methacrylate and 1 mmol of2,2′-azobis(2-amidinopropane) dihydrochloride to obtain insulatingparticles [2] having an average particle-size of 210 nm and a CV valueof the particle size of 13%, with an amidino group and an epoxy groupbeing contained in the surface thereof.

(3) Preparation of Insulating Particles [3]

Into 500 mL of dehydrated ethanol in a separable flask (1000 mL)equipped with a four-neck separable cover, a stirring blade, a three-waystopcock was dissolved 100 mmol of 3-isocyanate propyltriethoxysilane.In this solution was dispersed 10 g of silica particles having aparticle size of about 200 nm in a nitrogen atmosphere, and stirred atroom temperature for 12 hours. Unreacted aminopropyltrimethoxysilane wasremoved therefrom by a centrifugal-separation washing process, and thedispersion medium was substituted from ethanol to toluene to prepare atoluene dispersion solution (solid component content 5%) of insulatingparticles [3] with an isocyanate group being contained in the surfacethereof.

(4) Preparation of Insulating Particles [4]

The same preparation processes as the insulating particles [1] werecarried out except that the monomer composition was changed to contain50 mmol of glycidyl methacrylate, 50 mmol of methyl methacrylate, 3 mmolof ethylene glycol dimethacrylate, 1 mmol of methacrylic acidphenyldimethylsulfoniummethyl sulfate and 2 mmol of2,2′-azobis{2-[N-(2-carboxyethyl)amidino]propane} to prepare insulatingparticles [4] having an average particle-size of 180 nm and a CV valueof the particle size of 7%, with a sulfonium group and an epoxy groupbeing contained in the surface thereof.

(5) Preparation of Insulating Particles [5]

The same preparation processes as the insulating particles [1] werecarried out except that the monomer composition was changed to contain100 mmol of isobutyl methacrylate, 3 mmol of ethylene glycoldimethacrylate, 3 mmol of methacrylic acid phenyldimethylsulfoniummethylsulfate and 1 mmol of 2,2′-azobis{2-[N-(2-carboxyethyl) amidino]propane}to prepare insulating particles [5] having an average particle-size of190 nm and a CV value of the particle size of 11%, with a sulfoniumgroup being contained in the surface thereof.

(6) Preparation of Insulating Particles [6]

The same preparation processes as the insulating particles [1] werecarried out except that the monomer composition was changed to contain100 mmol of t-butyl methacrylate, 5 mmol of ethylene glycoldimethacrylate, 1 mmol of N,N,N-trimethyl-N-2-methacryloyloxyethylammonium chloride and 1 mmol of 2,2′-azobis(2-amidinopropane)dihydrochloride to prepare insulating particles [6] having an averageparticle-size of 210 nm and a CV value of the particle size of 13%, withan ammonium group being contained in the surface thereof.

(7) Preparation of Insulating Particles [7]

The same preparation processes as the insulating particles [1] werecarried out except that the monomer composition was changed to contain50 mmol of glycidyl methacrylate, 50 mmol of styrene, 10 mmol ofethylene glycol dimethacrylate, 10 mmol of divinyl benzene, 1 mmol ofmethacrylic acid phenyldimethylsulfoniummethyl sulfate and 2 mmol of2,2′-azobis{2-[N-(2-carboxyethyl) amidino]propane} to prepare insulatingparticles [7] having an average particle-size of 190 nm and a CV valueof the particle size of 10%, with a sulfonium group and an epoxy groupbeing contained in the surface thereof.

(8) Preparation of Insulating Particles [8]

The same preparation processes as the insulating particles [1] werecarried out except that the monomer composition was changed to contain500 mmol of styrene, 2 mmol of sodium p-styrene sulfonate, 1 mmol ofpotassium persulfate and that distilled water was added thereto to setthe solid component content to 10% by weight to prepare insulatingparticles [8] having an average particle-size of 120 nm and a CV valueof the particle size of 10%, with a sulfonic acid group being containedin the surface thereof.

2. Preparation of Metal Surface Particles [1] and [2]

(1) Preparation of Metal Surface Particles [1]

Core particles made from tetramethylol methane tetracrylate/divinylbenzene having an average particle size of 5 μm were subjected todefatting, sensitizing and activating processes to form Pd cores on thesurface of core particles so as to form catalyst cores for electrolessplating. Next, these particles were immersed into an electroless Niplating bath that has been initially prepared and heated in accordancewith a predetermined method so that a Ni plated layer was formed. Next,the surface of the nickel layer was subjected to an electrolesssubstitution gold plating process to prepare metal-surface particles.The resulting metal surface particles have a Ni-plating thickness of 90nm and a gold plating thickness of 30 nm.

(2) Preparation of Metal Surface Particles [2]

To 1000 mL of methanol in a separable flask (2000 mL) equipped with afour-neck separable cover, a stirring blade and a three-way stopcock wasadded and dissolved 20 mmol of 2-aminoethane thiol to prepare a reactionsolution.

In the reaction solution were dispersed 20 g of metal surface particles[1] under a nitrogen atmosphere and stirred at room temperature for 3hours, and unreacted 2-aminoethane thiol was removed therefrom by afiltering process, and the resulting matter was washed with methanol,and dried to prepare metal surface particles [2] with an amino groupserving as a reactive functional group being contained in the surfacethereof.

3. Preparation of Coated Conductive Particles

EXAMPLE 1

Insulating particles [1] were dispersed in distilled water underirradiation with ultrasonic wave to obtain an aqueous dispersionsolution having 10% by weight of insulating particles [1].

In 500 mL of distilled water were dispersed 10 g of metal surfaceparticles [1], and to this was added 4 g of aqueous dispersion solutionof insulating particles [1], and stirred at room temperature for 6hours. After having been filtered through a mesh-filter of 3 μm, thiswas further washed with methanol, and dried to obtain coated conductiveparticles [1].

When each of coated conductive particles [1] was observed under ascanning electronic microscope (SEM), only one coating layer was formedon the surface of each of metal surface particles [1] by insulatingparticles [1]. When the coated area (that is, the projection area of theparticle size of each insulating particle) of the insulating particleswith respect to an area of 2.5 μm from the center of the coatedconductive particle was calculated by an image analysis, a coating rateof 30% was obtained. Moreover, a cross-sectional observation by atransmission electronic microscope (TEM) showed that a bonding interfacebetween the insulating particles and the metal surface particle was 12%of the circumference of the insulating particle; therefore, theinterface bonding area to the metal surface particle was 12% of thesurface area of the insulating particle.

Coated conductive particles [1] were dispersed in t-butyl alcohol, andweighed so that after the drying process, the weight of the coatedconductive particles was set to 0.00004 g (about 240,000 particles) per10×10 mm on a silicon wafer, and after the drying process, a siliconwafer of 10×10 mm was put thereon, and after having been heated at 200°C. for 30 seconds under a pressure of 100 N, the silicon wafer waspulled and separated therefrom. When the state of the insulatingparticles on the surface of the coated particle was observed under anSEM, it was found that the metal surface of metal surface particles [1]was exposed due to fused insulating particles [1] with particlesadhering onto the silicon wafer side being also fused.

The results of these tests are shown in Table 1.

EXAMPLE 2

Insulating particles [2] were dispersed in acetone under irradiationwith ultrasonic wave to obtain an acetone dispersion solution having 10%by weight of insulating particles [2].

In 500 mL of acetone were dispersed metal surface particles [1], and tothis was added 4 g of acetone dispersion solution of insulatingparticles [2], and stirred at room temperature for 12 hours. Afterhaving been filtered through a mesh-filter of 3 μm, this was furtherwashed with methanol, and dried to obtain coated conductive particles[2].

In coated conductive particles [2], only one coating layer was formed onthe surface of each of metal surface particles [1] by insulatingparticles [2]. When measured in the same method as example 1, thecoating rate thereof was 70%, and the interface bonding area was 15% ofthe surface area of the insulating particle. Moreover, when the statethereof after having been thermocompression-bonded between siliconwafers was observed under an SEM in the same method as example 1, it wasfound that the metal surface of metal surface particles [1] was exposeddue to fused insulating particles [2] with particles adhering onto thesilicon wafer side being also fused.

The results of these tests are shown in Table 1.

EXAMPLE 3

Insulating particles [3] were dispersed in toluene under irradiationwith ultrasonic wave to obtain a toluene dispersion solution having 10%by weight of insulating particles [3].

In 500 mL of toluene were dispersed metal surface particles [2], and tothis was added 4 g of the toluene dispersion solution of insulatingparticles [3], and stirred at room temperature for 4 hours. After havingbeen filtered through a mesh-filter of 3 μm, this was further washedwith acetone, and dried to obtain coated conductive particles [3].

In coated conductive particles [3], only one coating layer was formed onthe surface of each of metal surface particles [2] by insulatingparticles [3]. When measured in the same method as example 1, thecoating rate thereof was 40%, and the interface bonding area was 5% ofthe surface area of the insulating particle. Moreover, when the statethereof after having been thermocompression-bonded between siliconwafers was observed under an SEM in the same method as example 1, it wasfound that the metal surface of metal surface particles [2] was exposeddue to separation of insulating particles [3], and some separatedinsulating particles [3] were observed on the periphery of each coatedconductive particle.

The results of these tests are shown in Table 1.

EXAMPLE 4

Insulating particles [4] were dispersed in acetone under irradiationwith ultrasonic wave to obtain an acetone dispersion solution having 10%by weight of insulating particles [4].

In 500 mL of acetone were dispersed metal surface particles [2], and tothis was added 1 g of the acetone dispersion solution of insulatingparticles [4], and stirred at room temperature for one hour. Afterhaving been filtered through a mesh-filter of 3 μm, this was furtherwashed with methanol, and dried to obtain coated conductive particles[4].

In coated conductive particles [4], only one coating layer was formed onthe surface of each of metal surface particles [2] by insulatingparticles [4]. When measured in the same method as example 1, thecoating rate thereof was 8%, and the interface bonding area was 12% ofthe surface area of the insulating particle. Moreover, when the statethereof after having been thermocompression-bonded between siliconwafers was observed under an SEM in the same method as example 1, it wasfound that the metal surface of metal surface particles [2] was exposeddue to deformation of insulating particles [4], with insulatingparticles [4] adhering onto the silicon wafer side being also deformed.However, neither fused insulating particles [4] nor separated insulatingparticles [4] were found.

The results of these tests are shown in Table 1.

EXAMPLE 5

By using the same method as example 4, an acetone dispersion solutionhaving 10% by weight of insulating particles [4] was obtained.

In 500 mL of acetone were dispersed metal surface particles [2], and tothis was added 3 g of the acetone dispersion solution of insulatingparticles [4], and stirred at room temperature for 3 hours. After havingbeen filtered through a mesh-filter of 3 μm, this was further washedwith methanol, and dried to obtain coated conductive particles [5].

In coated conductive particles [5], only one coating layer was formed onthe surface of each of metal surface particles [2] by insulatingparticles [4]. When measured in the same method as example 1, thecoating rate thereof was 20%, and the interface bonding area was 12% ofthe surface area of the insulating particle. Moreover, when the statethereof after having been thermocompression-bonded between siliconwafers was observed under an SEM in the same method as example 1, it wasfound that the metal surface of metal surface particles [2] was exposeddue to deformation of insulating particles [4], with insulatingparticles [4] adhering onto the silicon wafer side being also deformed.However, neither fused insulating particles [4] nor separated insulatingparticles [4] were found.

The results of these tests are shown in Table 1.

EXAMPLE 6

By using the same method as example 4, an acetone dispersion solutionhaving 10% by weight of insulating particles [4] was obtained.

In 500 mL of acetone were dispersed metal surface particles [2], and tothis was added 4 g of the acetone dispersion solution of insulatingparticles [4], and stirred at room temperature for 6 hours. After havingbeen filtered through a mesh-filter of 3 μm, this was further washedwith methanol, and dried to obtain coated conductive particles [6].

In coated conductive particles [6], only one coating layer was formed onthe surface of each of metal surface particles [2] by insulatingparticles [4]. When measured in the same method as example 1, thecoating rate thereof was 40%, and the interface bonding area was 12% ofthe surface area of the insulating particle. Moreover, when the statethereof after having been thermocompression-bonded between siliconwafers was observed under an SEM in the same method as example 1, it wasfound that the metal surface of metal surface particles [2] was exposeddue to deformation of insulating particles [4], with insulatingparticles [4] adhering onto the silicon wafer side being also deformed.However, neither fused insulating particles [4] nor separated insulatingparticles [4] were found.

The results of these tests are shown in Table 1.

EXAMPLE 7

Insulating particles [5] were dispersed in acetone under irradiationwith ultrasonic wave to obtain an acetone dispersion solution having 10%by weight of insulating particles [5].

In 500 mL of acetone were dispersed metal surface particles [1], and tothis was added 4 g of the acetone dispersion solution of insulatingparticles [5], and stirred at room temperature for 6 hours. After havingbeen filtered through a mesh-filter of 3 μm, this was further washedwith methanol, and dried to obtain coated conductive particles [7].

In coated conductive particles [7], only one coating layer was formed onthe surface of each of metal surface particles [1] by insulatingparticles [5]. When measured in the same method as example 1, thecoating rate thereof was 30%, and the interface bonding area was 12% ofthe surface area of the insulating particle. Moreover, when the statethereof after having been thermocompression-bonded between siliconwafers was observed under an SEM in the same method as example 1, it wasfound that the metal surface of metal surface particles [1] was exposeddue to deformation of insulating particles [5], with insulatingparticles [5] adhering onto the silicon wafer side being also deformed.However, neither fused insulating particles [5] nor separated insulatingparticles [5] were found.

The results of these tests are shown in Table 1.

EXAMPLE 8

Insulating particles [6] were dispersed in acetone under irradiationwith ultrasonic wave to obtain an acetone dispersion solution having 10%by weight of insulating particles [6].

In 500 mL of acetone were dispersed metal surface particles [1], and tothis was added 4 g of the acetone dispersion solution of insulatingparticles [6], and stirred at room temperature for 6 hours. After havingbeen filtered through a mesh-filter of 3 μm, this was further washedwith methanol, and dried to obtain coated conductive particles [8].

In coated conductive particles [8], only one coating layer was formed onthe surface of each of metal surface particles [1] by insulatingparticles [6]. When measured in the same method as example 1, thecoating rate thereof was 30%, and the interface bonding area was 10% ofthe surface area of the insulating particle. Moreover, when the statethereof after having been thermocompression-bonded between siliconwafers was observed under an SEM in the same method as example 1, it wasfound that the metal surface of metal surface particles [1] was exposeddue to deformation of insulating particles [6], with insulatingparticles [6] adhering onto the silicon wafer side being also deformed.However, neither fused insulating particles [6] nor separated insulatingparticles [6] were found.

The results of these tests are shown in Table 1.

EXAMPLE 9

Insulating particles [7] were dispersed in acetone under irradiationwith ultrasonic wave to obtain an acetone dispersion solution having 10%by weight of insulating particles [7].

In 500 mL of acetone were dispersed metal surface particles [2], and tothis was added 4 g of the acetone dispersion solution of insulatingparticles [7], and stirred at room temperature for 5 hours. After havingbeen filtered through a mesh-filter of 3 am, this was further washedwith methanol, and dried to obtain coated conductive particles [9].

In coated conductive particles [9], only one coating layer was formed onthe surface of each of metal surface particles [2] by insulatingparticles [7]. When measured in the same method as example 1, thecoating rate thereof was 35%, and the interface bonding area was 8% ofthe surface area of the insulating particle. Moreover, when the statethereof after having been thermocompression-bonded between siliconwafers was observed under an SEM in the same method as example 1, it wasfound that the metal surface of metal surface particles [2] was exposeddue to deformation of insulating particles [7], with insulatingparticles [7] adhering onto the silicon wafer side being also deformed.However, neither fused insulating particles [7] nor separated insulatingparticles [7] were found.

The results of these tests are shown in Table 1.

COMPARATIVE EXAMPLE 1

Insulating particles [8] were dispersed in distilled water underirradiation with ultrasonic wave to obtain an aqueous dispersionsolution having 10% by weight of insulating particles [8].

In 500 mL of distilled water were dispersed metal surface particles [1],and to this was added 4 g of the aqueous dispersion solution ofinsulating particles [8], and stirred at room temperature for 6 hours.After having been filtered through a mesh-filter of 3 μm, this wasfurther washed with methanol, and dried to obtain coated conductiveparticles [10].

In coated conductive particles [10], aggregated lumps of insulatingparticles [8] were formed on the surface of each of metal surfaceparticles [1]. When measured in the same method as example 1, thecoating rate thereof was 50%, and the interface bonding area was 12% ofthe surface area of the insulating particle. Moreover, when the statethereof after having been thermocompression-bonded between siliconwafers was observed under an SEM in the same method as example 1,insulating particles [8] on each of coated conductive particles [10]were fused; however, there were some coated conductive particles inwhich the metal surface of each of metal surface particles [1] was notexposed, and there were some particles adhering onto the silicon waferside that were not sufficiently fused. The reason for this is explainedas follows: in the case of coated conductive particles [10], sinceinsulating particles [8] form multiple layers, it is difficult to fusethese so as to be removed and it is also difficult to apply an uniformpressure onto the respective insulating particles [8].

The results of these tests are shown in Table 1.

COMPARATIVE EXAMPLE 2

To a hybridization system were loaded 1 g of vinylidene fluoride resinand 10 g of metal surface particles [1] so that these were subjected totreatments at 90° C. for 3 minutes to obtain coated conductive particles[11]

In coated conductive particles [11], a resin layer, made from thevinylidene fluoride resin, was formed on the surface of each of metalsurface particles [1]. When measured in the same method as example 1,the coating rate thereof was 60%. Moreover, when the state thereof afterhaving been thermocompression-bonded between silicon wafers was observedunder an SEM in the same method as example 1, the vinylidene fluorideresin on coated conductive particles [11] was completely fused so thatthe metal surface of each of metal surface particles [1] was exposed.

The results of these tests are shown in Table 1.

COMPARATIVE EXAMPLE 3

To a ball mill were loaded 1 g of silica particles used in forminginsulating particles [3] and 10 g of metal surface particles [1], andmixed for 20 minutes so as to allow these to electrostatically adhere toone another; thus, coated conductive particles [12] were obtained.

In coated conductive particles [12], only one layer of silica particleswas formed on the surface of each of metal surface particles [1]. Whenmeasured in the same method as example 1, the coating rate thereof was30%, and the interface bonding area was 5% of the surface area of theinsulating particle. Moreover, when the state thereof after having beenthermocompression-bonded between silicon wafers was observed under anSEM in the same method as example 1, it was found that the metal surfaceof metal surface particles [1] was exposed due to separation of thesilica particles, and there were some separated silica particles on theperiphery of each of the coated conductive particles.

The results of these tests are shown in Table 1.

COMPARATIVE EXAMPLE 4

The same processes as example 4 were carried out to prepare an acetonedispersion solution having 10% by weight of insulating particles [4].

In 500 mL of acetone were dispersed metal surface particles [2], and tothis was added 6 g of the acetone dispersion solution of insulatingparticles [4], and stirred at room temperature for 12 hours. Afterhaving been filtered through a mesh-filter of 3 μm, this was furtherwashed with methanol, and dried to obtain coated conductive particles[13].

In coated conductive particles [13], only one coating layer was formedon the surface of each of metal surface particles [2] by insulatingparticles [4]. When measured in the same method as example 1, thecoating rate thereof was 60%, and the interface bonding area was 12% ofthe surface area of the insulating particle. Moreover, when the statethereof after having been thermocompression-bonded between siliconwafers was observed under an SEM in the same method as example 1, it wasfound that although insulating particles [4] were deformed, there weresome coated conductive particles having metal surface particles [2]whose metal surface was not exposed. This is presumably because the highcoating density of the insulating particles or the multilayered coatingstructure thereof makes it difficult for the metal surface to beexposed.

The results of these tests are shown in Table 1.

COMPARATIVE EXAMPLE 5

To a ball mill were loaded 1 g of insulating particles [4] and 10 g ofmetal surface particles [1], and mixed for 20 minutes so as to allowthese to electrostatically adhere to one another; thus, coatedconductive particles [14] were obtained.

In coated conductive particles [14], 1 to 3 coated layers were formed onthe surface of each of metal surface particles [1] by insulatingparticles [4]. When measured in the same method as example 1, thecoating rate thereof was 30%, and the interface bonding area was 8% ofthe surface area of the insulating particle. Moreover, when the statethereof after having been thermocompression-bonded between siliconwafers was observed under an SEM in the same method as example 1, it wasfound that although some of insulating particles [4] were deformed, manyof them were separated with the metal surface of metal surface particles[1] being exposed, and there were some separated insulating particles onthe periphery of each of the coated conductive particles.

The results of these tests are shown in Table 1.

COMPARATIVE EXAMPLE 6

To a hybridization system were loaded 1 g of insulating particles [4]and 10 g of metal surface particles [2] so that these were subjected totreatments at 120° C. for 3 minutes to obtain coated conductiveparticles [15].

In coated conductive particles [15], insulating particles [4] coveringthe surface of each of metal surface particles [2] were deformed by heatand impact, and the coated layer was formed by multiple layers. Whenmeasured in the same method as example 1, the coating rate thereof was70%, and the interface bonding area was 40% of the surface area of theinsulating particle. Moreover, when the state thereof after having beenthermocompression-bonded between silicon wafers was observed under anSEM in the same method as example 1, it was found that althoughinsulating particles [4] were deformed, there were some coatedconductive particles having metal surface particles [2] whose metalsurface was not exposed. This is presumably because the high coatingdensity of the insulating particles or the multilayered coatingstructure thereof makes it difficult for the metal surface to beexposed.

The results of these tests are shown in Table 1. TABLE 1 State of Metalsurface Insulating Coating Bonding insulating particles particlesparticles rate (%) area (%) Coated state upon contact bonding Example 11 1 30 12 Single layer Fused Example 2 1 2 70 15 Single layer FusedExample 3 2 3 40  5 Single layer Separated Example 4 2 8  8 12 Singlelayer Deformed Example 5 2 4 20 12 Single layer Deformed Example 6 2 440 12 Single layer Deformed Example 7 1 5 30 12 Single layer DeformedExample 8 1 6 30 10 Single layer Deformed Example 9 2 7 35  8 Singlelayer Deformed Comparative 1 8 50 12 Multi-layer Fused (partiallyExample 1 separated) Comparative 1 Vinylidene 60 — — Fused Example 2flouride resin Comparative 1 Silica 30  5 Single layer Separated Example3 particles Comparative 2 4 60 12 Single layer Deformed Example 4Comparative 1 4 30  8 Multi-layer Partially deformed Example 5 andseparated Comparative 2 4 70 40 Multi-layer Deformed Example 64. Preparation of Anisotropic Conductive Material

EXAMPLE 10

Epoxy resin (“Epicoat 828”: made by Yuka Shell Epoxy Co., Ltd.)(100parts) serving as a binder resin and trisdimethyl aminoethyl phenol andtoluene (100 parts) were sufficiently dispersed and mixed by using aplanetary stirring device, and this was applied onto a releasing filmwith a fixed thickness so as to form a thickness of 10 μm after drying,and toluene was evaporated so that an adhesive film without containingcoated conductive particles was obtained.

Moreover, to the epoxy resin (“Epicoat 828”: made by Yuka Shell EpoxyCo., Ltd.)(100 parts) serving as a binder resin and trisdimethylaminoethyl phenol and toluene (100 parts) were added coated conductiveparticles [1], and this was sufficiently dispersed and mixed by using aplanetary stirring device to prepare a binder resin dispersion matter,and this was then applied onto a releasing film with a fixed thicknessso as to form a thickness of 7 μm after drying, and toluene wasevaporated so that an adhesive film containing coated conductiveparticles [1] was obtained. Here, the added amount of the coatedconductive particles [1] was set so that the content thereof in ananisotropic conductive film [1] was 200,000 particles/cm².

The adhesive film without containing coated conductive particles waslaminated on the resulting adhesive film containing coated conductiveparticles [1] at room temperature so that an anisotropic conductive film[1] having a thickness of 17 μm, which had a two-layer-structure, wasobtained.

Here, one portion of the binder resin dispersion matter containingcoated conductive particles [1] was washed with toluene so that coatedconductive particles [1] were extracted; thereafter, when the resultingparticles were observed under an SEM, no separation of the insulatingparticles from the coated conductive particles was confirmed.

EXAMPLES 11 TO 18, COMPARATIVE EXAMPLES 7 TO 12

The same processes as example 10 were carried out except that coatedconductive particles [2] to [15], obtained in examples 2 to 9 andcomparative examples 1 to 6, were respectively used so that anisotropicconductive films [2] to [15] were obtained. The thickness of all theanisotropic conductive films was set to 17 μm, with the content of allthe coated conductive particles being set to 200,000 particles/cm².

Here, one portion of the binder resin dispersion matter containingcoated conductive particles was washed with toluene so that coatedconductive particles were extracted; thereafter, when the resultingparticles were observed under an SEM, no separation of the insulatingparticles from the coated conductive particles was confirmed. However,in the case of coated conductive particles [10], although the laminatedstructure no longer existed to virtually form a single coated filmpresumably because the laminated insulating particles were separatedtherefrom, the coating rate increased from 50% to 70%. This ispresumably because the separated insulating particles re-adhered to thesurface. Further, in the case of the coated conductive particles [12]and [14], the coating rates decreased from 30% to less than 5%respectively presumably due to coming off during the dispersing process.

With respect to the anisotropic conductive films [1] to [15] obtained inexamples 10 to 18 and comparative examples 7 to 12, evaluation wasconducted on insulating/conductivity properties and adhesion. Theresults of evaluation are shown in Table 2.

(Insulating Property Test Between Adjacent Electrodes)

Pieces of an anisotropic conductive film, cut into a size of 4×18 mm,were bonded onto a silicon wafer circuit board having a comb-shapedpattern represented in FIG. 1 (number of lines: 400, length ofoverlapped portions: 2 mm, line width: 20 μm, line interval: 20 μm, lineheight: 18 μm), and this was sandwiched between flat glass plates havinga size of 2×12.5 mm and a thickness of 1 mm, and subjected tothermocompression bonding processes under the following conditions 1 and2; thereafter, a resistance value between the electrodes was measuredand the rate of values of not less than 10⁸Ω was found. The presenttests were carried out under n=20.

Condition 1: heating process for 30 minutes at 150° C. under an appliedpressure of 20 N.

Condition 2: heating process for 30 seconds at 200° C. under an appliedpressure of 200 N.

(Longitudinal Conductivity Tests)

Pieces of an anisotropic conductive film, cut into a size of 5×5 mm,were bonded virtually in the center of one of glass circuit boards(width: 1 cm, length: 2.5 cm) on which ITO electrodes (width: 100 μm,height: 0.2 μm, length: 2 cm) were formed; thereafter, a glass circuitboard having the same ITO electrodes was positioned thereon with themutual electrodes being overlapped with 90 degrees, and bonded to eachother. After the joined portions of the glass circuit boards had beenthermocompression-bonded under condition 1 and condition 2, theresistance value was measured by using a four-terminal method and therate of values of not more than 5Ω was found. The present tests werecarried out under n=20.

Condition 1: heating process for 30 minutes at 150° C. under an appliedpressure of 20 N

Condition 2: heating process for 30 seconds at 200° C. under an appliedpressure of 200 N.

Moreover, with respect to the anisotropic conductive films [2], [6], [8]and [11], glass circuit boards that had been thermocompression-bondedunder condition 1 were left for 300 hours under cycles of 55° C.×6 hoursand 120° C.×6 hours; thereafter, the resistance value was measured byusing a four-terminal method, and the rate of values of not more than 5Ωwas found, and defined as the conductivity after 300 hours.

(Evaluation of Adhesion)

With respect to the anisotropic conductive films [2], [6], [8] and [11],longitudinal conductivity tests were carried out under condition 1, andafter these test circuit boards had been further left for 300 hoursunder cycles of 55° C.×6 hours and 120° C.×6 hours, the cross-sectionthereof was observed under an SEM for any interface separation betweenthe conductive particles and the insulating particles as well as betweenthe insulating particles and the binder resin. TABLE 2 Adhesionevaluation Between Coated Between metal insulating conductive Separationof Insulating property test Conductivity test surface particlesparticles fine binder resin 20 N 200 N 20 N 200 N After and insulatingand binder particles upon dispersion 150° C. 30 m 200° C. 30 s 150° C.30 m 200° C. 30 s 300 h particles resin Example 10 1 No  95%  90% 100%100% — — — Example 11 2 No 100%  95%  85%  90%  90% No No interfaceinterface separation separation Example 12 3 No 100% 100%  90% 100% — —— Example 13 4 No  90%  85% 100% 100% — — — Example 14 5 No 100%  95%100% 100% — — — Example 15 6 No 100% 100% 100% 100% 100% No No interfaceinterface separation separation Example 16 7 No 100% 100% 100% 100% — —— Example 17 8 No 100% 100% 100% 100% 100% Only slight Slight interfaceinterface separation separation Example 18 9 No 100% 100%  90% 100% — —— Comparative 10 Yes (increase 100% 100%  70%  80% — — — Example 7 incoat density) Comparative 11 No  60%  60% 100% 100%  50% InterfaceInterface Example 8 separation in separation some substrates in almostall the substrates Comparative 12 Yes (decrease  10%  5% 100% 100% — — —Example 9 in coat density) Comparative 13 No 100% 100%  50%  80% — — —Example 10 Comparative 14 Yes (decrease  30%  10% 100% 100% — — —Example 11 in coat density) Comparative 15 No 100% 100%  40%  60% — — —Example 12

INDUSTRIAL APPLICABILITY

In accordance with the present invention, it becomes possible to providea coated conductive particle having superior connection reliability, amethod for manufacturing such coated conductive particle, an anisotropicconductive material and a conductive-connection structure.

1. A coated conductive particle comprising a particle having a surfacemade of conductive metal and an insulating particles to coat the surfaceof the particle having the surface made of conductive metal there with,wherein the insulating particles are chemically bonded to the particlehaving the surface made of conductive metal via a functional group (A)having a bonding property to the conductive metal so that a singlecoating layer is formed.
 2. The coated conductive particle according toclaim 1, wherein the particle having the surface made of conductivemetal comprises a core particle made from a resin and a conductive metallayer formed on the surface of the core particle.
 3. The coatedconductive particle according to claim 1, wherein 5 to 50% of thesurface area of the particle having the surface made of conductive metalis coated with the insulating particles.
 4. The coated conductiveparticle according to claim 1, wherein the insulating particles have anaverage particle size of not more than 1/10 of the average particle sizeof the particle having the surface made of conductive metal.
 5. Thecoated conductive particle according to claim 1, wherein the insulatingparticles have a CV value of the particle size of not more than 20%. 6.The coated conductive particle according to claim 1, wherein theinsulating particles are brought into contact with the surface of theparticle having the surface made of conductive metal at not more than20% of the surface area.
 7. The coated conductive particle according toclaim 1, wherein the insulating particles are softer than the particlehaving the surface made of conductive metal.
 8. The coated conductiveparticle according to claim 7, wherein the insulating particles are madefrom a cross-linking resin.
 9. The coated conductive particle accordingto claim 1, wherein the insulating particles are harder than theparticle having the surface made of conductive metal.
 10. The coatedconductive particle according to claim 1, wherein the insulatingparticles have a positive charge.
 11. The coated conductive particleaccording to claim 1, wherein the insulating particles are made from aresin having an ammonium group or a sulfonium group.
 12. The coatedconductive particle according to claim 1, wherein the functional group(A) having a bonding property to metal is a thiol group or a sulfidegroup.
 13. A method for manufacturing the coated conductive particleaccording to claim 1, which comprises at least the steps of: a step 1 ofallowing insulating particles to aggregate onto the particle having thesurface made of conductive metal by a Van der Waals force or anelectrostatic interaction in an organic solvent and/or water; and a step2 of chemically bonding the particle having the surface made ofconductive metal and the insulating particles to each other.
 14. Ananisotropic conductive material, wherein the coated conductive particleaccording to claim 1, is dispersed in an insulating binder resin. 15.The anisotropic conductive material according to claim 14, wherein thebinder resin is an adhesive being cured by heat and/or light.
 16. Theanisotropic conductive material according to claim 14 wherein thefunctional group belonging to the insulating particles of the coatedconductive particle is chemically bonded to the functional group in thebinder resin.
 17. The anisotropic conductive material according to claim16, wherein the functional group belonging to the insulating particlesof the coated conductive particle to be chemically bonded to thefunctional group in the binder resin is an epoxy group.
 18. Theanisotropic conductive material according to claim 14, which is ananisotropic conductive adhesive.
 19. A conductive-connection structure,which is conduction-connected by the coated conductive particleaccording to claim
 1. 20. A conductive-connection structure, which isconduction-connected by anisotropic conductive material according toclaim 14.